<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>
    <style>
        .test_div {
            /*border: 1px solid rgba(0, 0, 0, 0.125);*/
            /*box-shadow: 2px 2px rgba(0, 0, 0, .6);*/
            box-shadow: 4px 4px 10px #888888;
            z-index: 10;
            /*overflow: auto;*/
            margin-top: -16px;
            margin-left: -2px;
            height: 100px;
            max-height: 200px;
            width: 780px;
            position: absolute;
            display: none;
        }
    </style>
</head>
<body>
<div style="position: relative">
    <div style="background-color: #0c5460; height: 100px; " class="test_div" id="test_id"></div>
</div>

<script>
    // $('div').show();
    // $('#test_id').show();
    //$('.test_div').show();
</script>
</body>
body...
</html>
html...